This invention relates to a process for preparing graft copolymers of cellulose derivatives and N,N-diallyl-N,N-dialkylammonium halides. More particularly, the invention relates to the preparation of such graft copolymers in a dry or substantially solvent-free system.
Graft copolymers of polysaccharides such as starches, cellulose and gums are known in the literature and find uses in a variety of applications including as paper filler retention aids, adhesives, sizings, flocculants, ion exchange resins, drilling and mud additives and water treatment aids. In particular, graft copolymers of cellulose derivatives and N,N-diallyl-N,N-dialkyl ammonium halides have been recognized as superior conditioners in the formulation of shampoos and rinses for application to human hair.
Heretofore, methods employed for the production of such graft copolymers as represented by the teachings of U.S. Pat. Nos. 3,809,664 and 3,976,552, include polymerizations in water, in water-solvent mixtures and in the dry state, and may be initiated by mechanical, chemical and irradiative techniques.
Most of the above-described methods, however, are relatively unsuited for the efficient grafting of water soluble monomers in aqueous environments where polymerization with these monomers would be most desirable, particularly when chemical initiators are employed. This inefficient grafting is mainly due to the strong tendency of these monomers to form separate non-graft polymers in the aqueous phase. For efficient grafting, it is necessary to maintain the polysaccharide substrate and the water soluble monomer(s) in very close contact i.e. at high concentration with respect to the aqueous polymerization medium. In this manner, graft polymerization becomes the dominant reaction and the tendency to form non-graft polymers is minimized.
Several factors, however, prevent the grafting of water soluble monomers to polysaccharide substrates in highly concentrated aqueous environments. With water soluble or dispersed substrates like cellulose derivatives, gums and cooked starches, and the aqueous solution viscosities of even low concentrations (10-20%) of polysaccharide in water are prohibitively high and unmanageable. Thus it is not possible to graft a water soluble monomer, e.g. the N,N-diallyl-N,N-dialkyl ammonium halides to a soluble or dispersed cellulose substrate in water at, for example, 70% solids. With non-dispersed polysaccharide substrates like cellulose, which can be heterogeneously suspended in water at 40-60% solids, the graft product itself once produced in water will swell and exhibit very high viscosities during polymerization. This effect usually leads to coagulation of the reaction mixture making it commercially useless.
It has been proposed in U.S. Pat. No. 4,131,576 to overcome the above mentioned problems by suspending the polysaccharide in an organic polymerization solvent and adding thereto a water solution of the monomer to be grafted. In order to effect the required suspension, it is necessary that at least one of the phases (i.e. the suspended polysaccharide or the aqueous monomer solution) contain a suitable surfactant. While this method is generally satisfactory, it does possess two significant drawbacks. The use of substantial quantities of water and/or organic solvents necessitates costly and time-consuming isolation, washing, drying and solvent recovery steps. Moreover, in the embodiment wherein a water insoluble surfactant is employed, the presence of residual surfactant in the graft copolymer causes undesirable turbidity in any final aqueous products, e.g. hair care products, formulated therewith.
It is therefore an object of the present invention to provide a simple and efficient process for preparing graft copolymers of cellulose derivatives and N,N-diallyl-N,N-dialkyl ammonium halides.
It is also an object of the invention to provide such process wherein the graft polymerization may be carried out in a substantially dry environment requiring little or no water, solvent or water-insoluble surfactants.
It is a further object to provide a process for the production of such graft copolymers which can be isolated directly from the reaction mixture in dry form.